The subject matter disclosed herein relates generally to medical devices, and, more particularly, to a system and method for providing wireless power transmission to implantable electronic medical devices.
Implantable electronic medical devices, such as capsule endoscopes, cardiac implants, and blood-flow monitors have long been used in the medical profession for both diagnosis and treatment purposes. As these devices advance in both complexity and capability, they require more power to operate. Due to the location of these devices inside the human body, providing the required power has been difficult using existing methods.
Capsule endoscopy utilizes camera and lighting elements placed in a form factor suitable for a patient to swallow. The progression of the capsule endoscope through the patients gastrointestinal (GI) tract allows the capsule endoscope to capture images of the patients' GI tract. This examination of the GI tract allows physicians to examine and/or discover gastrointestinal bleeding, tumors of the small intestine, polyps, and Crohn's disease. Capsule endoscopy is beneficial as it is less invasive than traditional endoscopy for the patient, and allows for images to be captured of the small intestine which can be difficult with traditional endoscopy.
However, the viability of capsule endoscopy is limited by the power limitations inherent in the miniaturized devises. Currently, capsule endoscopes are battery powered and are typically limited to approximately eight hours of operating time. As the capsule endoscopes pass through the GI tract naturally via the patients peristaltic contractions, the capsule endoscope may not pass through the area of the GI tract of interest to the physician prior to the battery power being exhausted.
Other implanted medical devices including cardiac implants such as pacemakers and artificial hearts have additional issues associated with ensuring these devices have sufficient power. Currently, these cardiac devices rely on embedded batteries which can require surgery for battery replacement. Surgery, even routine, carries with it an inherent risk to the patient. In addition to this inherent risk, surgery is both uncomfortable and expensive for the patient.
To help address this issue, modern artificial hearts and pacemakers may contain rechargeable batteries that can be recharged using magnetic coupling. However, current magnetic coupling techniques require the charging circuit implanted in the body to be close to the surface of the skin. In the cases of cardiac implants, this can require lengths of wire to be placed close to the skin, sometimes within 1 cm, that are then connected to the implanted cardiac device. These wires are susceptible to reliability issues due to the dynamic nature of the human body which can cause the wires to frequently move, possibly leading to the wires being damaged or disconnected from the implanted device, which may required surgery to repair. Additionally, patients that have these wires implanted cannot undergo MRI scans due to the risk of RF heating causing injury to the patient.
Implantable blood flow monitors have similar limitations. Implantable blood flow monitors can either contain batteries having a finite amount of power or use transcutaneous transformers to wirelessly charge the devices. As with the cardiac implants, if the device is not located close to the surface of the skin, within approximately 1 cm, wires may need to be run from the device to the surface of the skin to allow for charging. This can lead reliability issues due to the movement of the wires along with the body, possibly leading to the wires being damaged or disconnected from the implanted device. Batteries, while replaceable, require additional surgery and can be prohibitively expensive for the patient.
While current technology does exist to wirelessly charge medical devices, it is limited in both its reliability and capability. As previously stated, current wireless power transmission systems may require the device, or the charging circuit, to be located close to the surface of the skin, typically within 1 cm. Additionally, the current designs of these transcutaneous transformer devices are very sensitive to the alignment of the transmission coil to the receiving coil. Precise coil alignment is needed to achieve maximum energy transfer. Improper alignment significantly reduces the power transfer. Finally, the small separation distance required between the transmission and receiving coils, combined with the requirement of coil alignment, means that current technology is not applicable to an ambulatory and deeply embedded device such as a capsule endoscope.
Modern wireless magnetic charging is further limited by the size of the transmission coil. A typical transmission coil for an artificial heart may be approximately 90 mm in diameter. While a 90 mm coil can transmit sufficient energy to charge an artificial heart, it requires that the receiving coil be located close to the skin surface, within approximately 1 cm, to ensure proper power transmission. To adequately transmit power deep into the body, where the device itself is located, requires approximately a 300 mm transmission coil. A coil of this size is capable of generating a uniform magnetic field deep within the body to charge the device without the requirement of wires run to near the surface of the skin. However, this is prohibitive as a coil of this size requires an extremely high voltage source in order to generate the required electrical current though the transmission coil due to the inductive impedance associated with a coil of the size described above. As an example, to provide a minimum 300 mW of power to operate a capsule endoscope located deep in the patients body, the required operating voltage of the coil may be as high as 3.5 kV. For powering an artificial heart requiring 10 W of power, the voltage would be many times higher. Due to the sensitivity of surrounding medical equipment and safety concerns for the patients and medical personnel, as well as high manufacturing and operating costs, the current solutions for wirelessly transmitting power to an implanted medical device are not feasible.
Thus, it can be seen that there is a need for the current invention, which can allow for charging medical devices located deep within the body without requiring high operational voltages to achieve the required power transfer.